Atherosclerosis is one of the leading causes of death in developed industrialized nations. Several experimental and epidemiological studies have established a link between toxic environmental or occupational chemicals and atherogenesis. Benzo(a)pyrene (BaP) has been demonstrated to induce smooth muscle cell (SMC) proliferation both in vivo and in vitro, a process which represents a hallmark of atherogenesis. BaP also increases the expression of c-Ha-ras, a protooncogene found in approximately 20% of human tumors, in cultured vascular SMCs. The proposed studies are designed to investigate the molecular mechanisms resulting in altered ras expression, which may contribute to establishment of a proliferative phenotype in BaP-treated SMCs. The DNA sequence elements mediating the BaP response will be identified using a complementary approach of mutational analysis and transient transfection assays, coupled to in vitro DNA- binding assays. Structure-activity relationships for c-Ha-ras induction will be defined through use of representative chemicals which are major BnP metabolites, induce oxidative stress, and/or are ligands of the Ah receptor. Molecular targets of BaP-inducible DNA-binding proteins will be identified using in vitro DNA-binding assays employing immunodepleted nuclear extracts and recombinant basal transcription factors. Elucidation of the mechanisms by which BaP modulates c-Ha-ras transcription may have significant implications for proliferative adaptations of treated SMCs, as well as for toxicant-induced atherosclerosis in humans.